THE 3 PARTS OF A MISTING SYSTEM

part 3: Misting Nozzles

A portable misting system cools off in the field

Every misting system has 3 basic components:

  • the misting pump
  • the lines & connectors


  • the mist nozzle, which we talk about here, also includes information on how to estimate water use.

How to Estimate the Water Use of a Misting System

How much water any misting system will use if often critical information for what kind and size of system you will use. There are 3 things you need to know to estimate water use for any misting system:

  1. The water pressure of the system
  2. The kind of nozzles your system will use, and
  3. How many nozzles the system will use

1. Water Pressure: The Quality of the Mist

The size of the water droplets that make up the mist helps determine how much cooling effect you'll be able to feel. As each little droplet evaporates, it cools the air immediately around it. Bigger droplets take (mili-seconds) longer to evaporate than smaller droplets. If they land on you before they've completely evaporated, you're wet. If you're in fairly dry air this can feel great as the water evaporates off of your skin. On the other hand, it can be uncomfortable in extremely humid weather, or if you just don't want to be wet. Also any water that doesn't evaporate must land on something. You'll need to make sure it doesn't puddle and that what it lands on is water-safe.

Smaller droplets evaporate mid-air. This is sometimes called "flash evaporation" because it happens "quick as a flash" and gives a stronger cooling effect. Also, smaller droplet can spread or "drift" more than larger droplets, cooling a larger area.

The lower pressure misting systems that yield larger water droplets also yield fewer water droplets. Fewer, larger water droplets around you cool the air unevenly. You can sometimes feel little spots of cool air surrounded by the unaffected hot air. It can feel like standing by a waterfall. The higher pressure misting systems that yield smaller droplets also yield more water droplets. The air is cooled more evenly and feels more like a fog. You are less likely to feel the warm air and more likely to simply feel the cooled air with these. Same amount of water, different number of droplets. Different cooling effects.

If the diameter of spray droplets is reduced by one-half, the number of droplets produced with a given volume is increased by eight times.
Doubling the droplet diameter will reduce the number produced by eight times.

Here is a sampling of water droplet sizes based on common nozzle sizes using 1000 psi / 70 bar. Water droplet sizes are measured in "microns" (1 micron is .001mm). To give you a size reference, 100 microns is about the diameter of a human hair. The largest of these droplets is just under half that.

.020" / .5 mm - the droplets range from 9.5 microns to 49.9 microns

.016" / .4 mm - the droplets range from 3.8 microns to 47.9 microns

.012" / .3 mm - the droplets range from 1.6 microns to 39.1 microns

.008" / .2 mm - the droplets range from 1.4 microns to 37.9 microns

.006" / .15 mm - the droplets range from 1.2 microns to 36.4 microns

Cooled air is heavier than the warm air. So the droplets evaporate above and around you and the cooled air drifts down onto you.

Once you know the water pressure you want to use you can pick out a mist nozzle.

Now you can look up misting nozzles on a flow rate chart. I'll use the general numbers from the flow rate chart below for an example, keeping in mind that numbers for any particular nozzle will vary from this. For this example I'll chose a nozzle that uses 13.5 GPH / 51.1 LPH

I'll mutiply that flow rate by the number of nozzles I want in the example system. For this example let's say 10 misting nozzles.
13.5 GPH / 51.1 LPH multiplied by 10 = 130.5 GPH / 510 LPH.

You can carry this a step further by estimating how many hours per day you'll use the system. Let's say 4 hours for this example.
130.5 GPH / 510 LPH multipied by 4 = 522 gallons / 2,040 liters per 4-hour day.

You can use this information to estimate water costs, too. See our page on Estimating Costs.


misting nozzles

The size of the mist nozzle orifice (opening) balances with your misting system's water pressure and flow rate (amount of water) to create a cooling mist. Every nozzle will spray less water at lower pressures than at high pressures. In fact, certain mist nozzles will not work at all at lower water pressures. As the water pressure at the nozzle increases, the flow rate through the nozzle increases. The higher the water pressure, the smaller the nozzle opening you'll need.

It will help to decide on the water pressure you want your system to use before selecting the mist nozzle.

The larger misting nozzles will work well with Low and Medium pressure misting systems. The smaller misting nozzles should only be used with High pressure systems. If you select too large a nozzle for your water pressure, the pump won't be able to send enough water through it to create a fine mist. If you select too small a nozzle, the over-supply of water through the nozzle may "over-pressure" the pump and damage it. It's not a matter of "more is better" but of balance.

.020" / .5 mm - for systems using very high water volume with less need for complete evaporation. Excellent for Low pressure misting systems

.016" / .4 mm - for systems where airflow and clearance allow for complete evaporation and where higher water volume is used. Good for Low and Medium pressure misting systems

.012" / .3 mm - most common and can be used for most systems. It can be used in both open and enclosed areas with complete evaporation. It provides similar results to the .008" nozzle but with more water (more "oomph"). Excellent for Medium pressure misting systems.

.008" / .2 mm - ideal for systems using less water volume with small droplet size, minimal moisture, and complete evaporation. Excellent for High pressure misting systems; won't work below 250 PSI / 17 bar.

.006" / .15 mm - ideal for systems using very low water volume with small droplet size, minimal moisture and complete evaporation. Only for High pressure misting systems. Won't work below 500 PSI / 34 bar.

Flow Rate

Misting nozzle manufacturers publish flow rates for their nozzles in gallons or liters per minute (GPM or LPM) or per hour (GPH or LPH) as it relates to different water pressures. Most spray nozzles are listed in a chart that shows their flow rate at one or more water pressure. An example chart is shown below. Note that some charts, like this one, are for general information -- these flow rates should not be assumed for any particular nozzle. Ask your nozzle supplier for charts on specific misting nozzles.

SIZE

PSI: 40 60 80 100 125 150 200 300 500 1000

BAR:

2.7

4.0

5.4

6.8

8.5

10

14

20

34

70

.020"/.5mm GPH 1.50 1.80 2.10 2.40 2.70 2.90 3.40 4.10 5.30 7.40

LPH

5.68

6.81

7.95

9.08

10.22

11.00

12.87

15.52

20.06

28.01

.016"/.16mm GPH 1.00 1.20 1.40 1.60 1.70 1.90 2.20 2.70 3.50 4.90

LPH

3.79

4.54

5.30

6.07

6.44

7.19

8.33

10.22

13.25

18.55

.012"/.3mm

GPH .750 .890 1.10 1.20 1.40 1.50 1.70 2.10 2.70 3.78

LPH

2.84

3.37

4.16

4.54

5.30

5.68

6.44

7.95

10.22

14.31

.008"/.2mm

GPH 1.05 1.35 1.89

LPH

3.97 5.11 7.15

.006"/.15mm

GPH 0.58 0.80
LPH 2.20 3.03

Differences in flow rate between nozzles sizes at lower pressures are smaller at lower pressures and bigger at higher pressures. Using the smallest nozzles your system's pressure can handle will minimize water use and costs while increasing the cooling effect. Notice that the smallest nozzles won't work with lower water pressures.

General Rule of Thumb: Nozzle flow for 500 psi / 34 bar equals 75% of the rated flow of 1000 psi / 70 bar;
nozzle flow for 250 psi / 17 bar equals 50% of the rated flow of 1000 psi / 70 bar.

A few mist nozzle options to consider:

Drain Valves will automatically drain the system each time it is turned off. This helps prevent nozzles plugging up due to calcium buildup, meaning much less nozzle cleaning needed. This is especially helpful for large systems or hard to reach nozzles.

Anti Drip Adapters will close each time the system is turned off to prevent dripping from the nozzles. Mist nozzle dripping may not be a problem if the water drips onto concrete or dirt. It could be a problem if it drips onto wood or machinery or guests.

Adjustable Angle Some mist nozzles can rotate or swivel to direct the spray in varying directions.

Materials Some mist nozzles are made with more durable materials than others. If yours will be a high pressure system that gets a lot of use, you'll probably want to consider higher quality nozzles. For example, stainless steel nozzles and nozzles with tungsten carbide orifices are more resistant to wear.

Nozzle Tees are the fittings that connect your nozzle to the line. You will need one of these for every nozzle. Select tees based on the size and material of your lines and your system's water pressure.

Some companies will give quantity discounts on nozzle tees and nozzles.

Spray Pattern / Mist Nozzle Spacing

misting nozzles are designed to create a spray that angles out anywhere from 40° - 100°, depending on your system's water pressure. The wider the angle, the more area the spray will cover and the fewer nozzles will be needed. 18, 24 or 30 inch nozzle spacing is standard, but some suppliers will customize spacing to your needs. Nozzle spacing in plastic, nylon, and copper lines can be easily customized during installation, too.

How far in the air the spray "drifts" or spreads is determined by their height off the ground, the system's water pressure and the size of the nozzle, plus the temperature of the water and the outside air.

For maximum cooling effect, it makes sense that you would want a fairly dense curtain of mist. But there is a point at which the system simply cannot make you any cooler, no matter how closely the nozzles are spaced. The final determination of how closely to space the misting nozzles in your system will be based on, well, your system.

Your system's water pressure, your choice of nozzles, your climate, even your system's configuration and the shape of the structure it is mounted to, all combine to make a system that is uniquely yours. Your misting system supplier's experience is invaluable in determining how far apart to space the nozzles. If installing it yourself, use one of the standard spacings and adjust it based on how many misting nozzles your system can handle. Spacing adjustments can be made after installation, if necessary. These adjustments will be easier to make in some line materials than others. Go back up to the section on flexible or rigid water lines or line materials if you'd like a review of this.

The number of misting nozzles any misting system can handle will vary depending on the pump, the type of nozzles used, corresponding flow rate, the number and types of fittings. Too many nozzles can cause a noticeable drop in performance. Most kits will tell you how many nozzles they can handle. Fewer nozzles mean less water used but more nozzles can mean more cooling. Remember, a misting system is a matter of balance.

Interested in learning even more?

  • To learn more about estimating misting system costs, see our page on Estimating Costs.
  • To compare misting systems with other outdoor coolinsg solutions, visit our comparison page.

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